The discovery of highly potent CGRP receptor antagonists

Article abstract of DOI:10.1016/j.bmcl.2008.10.106

Rational modification of a previously identified spirohydantoin lead structure has identified a series of potent spiroazaoxindole CGRP receptor antagonists. The azaoxindole was found to be a general replacement for the hydantoin that consistently improved

Full text of DOI:10.1016/j.bmcl.2008.10.106

Bioorganic & Medicinal Chemistry Letters 19 (2009) 214–217
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
The discovery of highly potent CGRP receptor antagonists
Craig A. Stump a, , Ian M. Bell , Rodney A. Bednar , Joseph G. Bruno , John F. Fay ,
a
a
a
a
*
a
b
b
a
a
Steven N. Gallicchio , Victor K. Johnston , Eric L. Moore , Scott D. Mosser , Amy G. Quigley ,
Christopher A. Salvatore , Cory R. Theberge , C. Blair Zartman , Xu-Fang Zhang , Stefanie A. Kane ,
Samuel L. Graham , Joseph P. Vacca , Theresa M. Williams
Department of Medicinal Chemistry, Merck & Co., Inc., PO Box 4, WP14-2, 770 Sumneytown Pike, West Point, PA 19486, USA
Department of Pain Research, Merck & Co., Inc., PO Box 4, West Point, PA 19486, USA
b
a
a
a
b
a
a
a
a
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Rational modification of a previously identified spirohydantoin lead structure has identified a series of
potent spiroazaoxindole CGRP receptor antagonists. The azaoxindole wasfound to be ageneral replacement
for the hydantoin that consistently improved in vitro potency. The combination of the indanylspiroazaox-
Received 18 September 2008
Revised 20 October 2008
Accepted 27 October 2008
Available online 31 October 2008
indole and optimized benzimidazolinones led to highly potent antagonists (e.g., 25, CGRP K
closely related compound 27 demonstrated good oral bioavailability in dog and rhesus.
i
= 40 pM). The
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords:
CGRP
Migraine
Headache
Migraine is a disabling neurovascular disorder that affects >10%
of the general population. A migraine attack is characterized by
receptor binding. A substantial boost in potency was achieved in
the benzodiazepinone series by incorporation of a hydrogen bond
acceptor adjacent to this NH (Scheme 1, 3 ? 4 ? 2). We postu-
lated that if the spirohydantoin and azabenzimidazolinone are
binding at a similar site on the receptor, an analogous potency
enhancing interaction might be achieved in the spirohydantoin
series with a similarly placed pyridine nitrogen (1 ? 12 ? 13).
Initially, a series of modifications to the hydantoin was explored
in order to evaluate the requirements for binding to the receptor
(Table 1). The compounds in the table were tested as racemic mix-
1
7
unilateral head pain and is often accompanied by phonophobia,
photophobia, and nausea. The current preferred method of treat-
ment involves the use of triptans, which activate 5-HT1B/1D recep-
tors. Although triptans are generally effective in the treatment of
migraines, they are contraindicated in patients with cardiovascular
2
disease due to their direct vasoconstrictive mode of action. Calci-
tonin gene-related peptide (CGRP), a 37 amino acid neuropeptide,
has been implicated in the pathogenesis of migraine.3 Clinical
studies have demonstrated the effectiveness of CGRP receptor
antagonists for the acute treatment of migraine with the intrave-
tures. Spirolactam 6 indicates that only the
a-carbonyl amide is
needed for CGRP receptor binding, as it maintained the potency
of the parent hydantoin 5. Addition of a second carbonyl to the lac-
tam provided imide 7, which offered a small potency enhance-
ment. Ring expansion to the valerolactam 8 led to a considerable
loss in potency, presumably by changing the trajectory of the crit-
4
nously-administered olcegepant and, more recently, with the
5
orally-administered telcagepant. Our research program continues
to focus on developing non-peptidic, orally bioavailable CGRP
receptor antagonists as novel therapeutics.
Previous communications from these laboratories described the
independent evolution of a high throughput screening lead into
two classes of potent CGRP receptor antagonists, represented by
6
,7
F C
O
1
and 2 (Fig. 1). Each compound exhibited good potency in both
3
NH
O
H
N
O
O
N
H
N
N
N
the radioligand binding assay and the cell-based functional assay,
however they both suffered from a significant loss of potency in
the cell-based assay in the presence of 50% human serum.
Despite the substantial structural diversity between these two
series, both contain a heterocyclic NH that is important for CGRP
NH
N
N
N
N
O
N
O
N
O
Me
1
2
Ki = 20 nM
cAMP IC50 = 78 nM
cAMP IC50 + 50% HS = 530 nM
Ki = 22 nM
cAMP IC50 = 49 nM
cAMP IC50 + 50% HS = 730 nM
*
Corresponding author. Tel.: +1 215 652 1775; fax: +1 215 652 7310.
E-mail address: craig_stump@merck.com (C.A. Stump).
Figure 1. Previously disclosed CGRP receptor antagonists.
0
960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.10.106

C. A. Stump et al. / Bioorg. Med. Chem. Lett. 19 (2009) 214–217
215
Table 1
F3C
O
NH
O
O
CGRP receptor affinity of spirohydantoin and related analogs.
N
O
O
H
N
NH
NH
N
N
N
N
N
N
O
N
N
O
H
R1
N
3
4
2
N
N
K
i = 520 nM
K
i = 2200 nM
K
i = 22 nM
N
O
R2
O
H
N
O
H
O
H
O
R1, R2
CGRP K
i
a,b
(nM)
N
N
Compound
NH
NH
NH
N
N
N
O
N
O
N
Me
O
1
12
13
NH
5
230 ± 28 (4)
270 ± 180 (8)
96 ± 45 (3)
K
i = 20 nM
•
N
O
H
Scheme 1. SAR trends in two series of CGRP receptor anatagonists.
O
ical amide binding motif. The dihydroimidazolinone 9, which has a
pendant phenyl substituent next to the amide, had improved po-
6
7
8
9
NH
•
tency (K
either a pyridine or cyclopropyl group resulted in a loss of activity
10 and 11). Fusion of the aromatic ring to produce oxindole 12
also led to a loss in potency (K = 520 nM), closely following the
i
= 34 nM). Replacement of the 2-phenyl substituent with
O
(
NH
i
•
O
SAR trend of the benzodiazepinone series (Scheme 1). Gratifyingly,
addition of the nitrogen to produce the spiroazaoxindole 13 re-
sulted in a substantial improvement in potency (K
The (S)-enantiomer (K = 2.3 nM) of the spiroazaoxindole 13
was much more potent than the (R)-enantiomer (K = 140 nM),
i
= 3.7 nM).
O
NH
NH
2700 ± 890 (4)
i
•
i
6
,8
consistent with previous results in the hydantoin series. Only
the (S)-enantiomers of the spiroazaoxindole will be discussed in
Table 2. The significant improvement in binding potency achieved
with the azaoxindole over the hydantoin was maintained in the
context of a variety of N-heteroaryl benzimidazolinones, a sam-
pling of which is shown in Table 2 [(S)-13 and 15 vs 1 and 14].
However, while this potency advantage was maintained in the
cell-based assay, much of it was lost with the addition of human
serum. A likely explanation is the higher affinity for plasma protein
of the more lipophilic azaoxindoles.
Potent CGRP receptor antagonists could also be prepared with
saturated heterocycles, either as an N-substituent on the benzimi-
dazolinone (17 and 19) or as a spiroheterocycle substituent on an
oxindole (21). These analogs exhibited a less pronounced serum
shift in the functional assay, leading to a significant improvement
in potency over 13. Modificationson thebenzimidazolinone that im-
proved intrinsic and functional potency were identified in the re-
O
34 (2)
•N
O
NH
1
0
130 ± 55 (3)
2600 ± 680 (4)
520 ± 280 (4)
3.7 ± 0.61 (3)
•N
N
O
NH
NH
11
•N
O
1
2
3
•
9
lated hydantoin series, providing compounds 22 and 24. The
incorporation of an optimized benzimidazolinone in the spiroazaox-
indole series led to the very potent 23, which had subnanomolar
potency in both the binding and functional assays, as well as nano-
molar potency in the presence of 50% human serum (IC50 = 4.1 nM).
Further optimization through constraint of the glycine side chain
produced an even more potent antagonist 25, which was the first
program analog with subnanomolar potency in the serum-shifted
functional assay (IC50 = 0.62 nM). Methylation of the constrained
O
NH
1
•
N
a
Mean value ± standard deviation, where appropriate; number of replicates in
parentheses.
b
Ki values for competition with 125I-hCGRP determined using membranes from
HEK293 cells stably expressing human CLR/RAMP1.5
i
glycine amide also produced a potent compound 27 (K = 0.23 nM),
albeit with reduced potency in the cell-based assay with human ser-
um (IC50 = 13 nM).
Calculated polar surface area (PSA) has been shown to correlate
with intestinal permeability.10 In a related series of spirohydantoin
compounds, an inverse relationship between PSA and bioavailabil-
sized in two steps from commercially available 4-nitrophthalic
acid following standard procedures. The SEM-protected azaoxin-
dole, which was prepared from commercially available 4-azaindole
6
ity has been observed. Consistent with this, the very potent analog
2
2
5, which has a high PSA (149 Å ), showed no oral bioavailability in
1
2
the dog. Moreover, the N-methyl analog 27, which has a reduced
using the methodology of Marfat, was bis-alkylated with the
dibromide to provide the racemic indanylspiroazaoxindole. Reduc-
tion of the nitro group and chiral resolution on a Chiralcel OD col-
umn was followed by a two step SEM-deprotection to provide the
desired (S)-aniline. The synthesis of the carboxylic acid intermedi-
2
PSA (134 Å ), displayed good oral bioavailability and low clearance
in the dog and rhesus (Table 3). However, 27 showed poor bioavail-
ability and increased clearance in the rat (F < 1%).
The synthesis of a representative compound (27) is outlined in
1
1
11
Scheme 2. 1,2-Bis(bromomethyl)-4-nitrobenzene was synthe-
ates have been reported elsewhere. The final amide coupling

2
16
C. A. Stump et al. / Bioorg. Med. Chem. Lett. 19 (2009) 214–217
Table 2
Comparison of CGRP receptor antagonist activity of spriroazaoxindoles and spirohydantoins.
H
O
H
O
N
N
A
NH
A
NH
N
O
O
N
Me
O
a,b
(nM) cAMP IC50a,c
nM)
cAMP IC50 + HSa,d
(nM)
a,b
(nM) cAMP IC50a,c
(nM)
cAMP IC50 + HSa,d
(nM)
A
Compound CGRP K
i
Compound CGRP K
i
(
O
N
N
1
20 ± 8 (7)
78 ± 23 (3)
530 ± (1)
(S)-13
2.3 ± 0.58 (3)
0.61 ± 0.26 (6)
1.2 (1)
8.6 ± 2.4 (4)
420 ± 180 (3)
N
O
N
O
N
N
14
16
18
16 ± 10 (5)
20 ± 3.6 (5)
13 ± 6.2 (3)
35 ± 6.4 (3)
1.7 (2)
10 (1)
74 (1)
15
1.6 (2)
35 (2)
N
O
N
N
61 ± 3.5 (3)
170 ± 97 (3)
220 (1)
160 (1)
23 (2)
17
5.2 (2)
27 (2)
H
O
S
N
N
27 (1)
19
0.87 ± 0.33 (4)
1.7 ± 0.88 (6)
0.21 ± 0.07 (6)
0.04 ± 0.008
2.5 (2)
24 (1)
O
O
N
2
2
0
2
57 (1)
21
5.7 (2)
39 (2)
O
O
Me
N
N
N
12 ± 7.1 (4)
23
0.87 ± 0.42 (3)
4.1 ± 0.22 (3)
Me
Me
O
Me
N
N
24
0.51 (1)
2.4 (2)
5.4 (2)
25
0.28 (2)
0.62 (2)
O
(
8)
HN
O
N
N
26
7.1 (2)
31 (1)
220 (1)
27
0.23 ± 0.078(8) 0.88 ± 0.20 (5)
13 ± 8.4 (5)
O
N
Me
a
b
c
Mean value ± standard deviation, where appropriate; number of replicates in parentheses.
125
5
K
i
values for inhibition of
I-hCGRP binding determined using membranes from HEK293 cells stably expressing human CLR/RAMP1.
5
Inhibition of CGRP-induced cAMP production in HEK293 cells stably expressing human CLR/RAMP1.
d
Inhibition of CGRP-induced cAMP production in HEK293 cells stably expressing human CLR/RAMP1in the presence of 50% human serum.5
Table 3
reaction was performed using EDC and HOBT to provide the target
compounds.
Pharmacokinetics of compound 27.
Species po dosea (mpk) iv doseb (mpk)
F (%) iv t1/2 (h) Cl (mL/min/kg)
In conclusion, rational design led to the development of a novel
series of potent indanylspiroazaoxindole CGRP receptor antago-
nists. The azaoxindole was found to be a general replacement for
the hydantoin that improved potency by an order of magnitude
in both the radioligand binding assay and the cell-based functional
assay. These studies led to the first program analog that was subn-
Rat
Dog
Rhesus
50
1
2
2
0.5
0.5
<1
58
35
0.99
2.6
1.8
30
3.8
7.5
a
Compound dosed in 90% PEG 400:10% water.
Compound dosed in DMSO.
b

C. A. Stump et al. / Bioorg. Med. Chem. Lett. 19 (2009) 214–217
217
O
O
of the more potent antagonists (27) displayed good bioavailability
in the dog and rhesus.
NH
N
2
O N
OH
OH
Acknowledgments
a, b
Br
c, d, e
O
The authors thank Dale Kling for the synthesis of 9 and 10;
Yvonne Leonard, Maria Stranieri-Michener, and Audrey Wallace
for animal dosing; Gary Adamson and Cynthia Miller-Stein for PK
analytical data; the MRL West Point analytical chemistry, mass
spectrometry, and NMR spectroscopy groups for analytical and
spectroscopic data; and Harold Selnick and Donnette Staas for
helpful discussions.
SEM
N
2
O N
N
Br
f
O
O
2
N
SEM
N
N
References and notes
1.
2.
3.
4.
Goadsby, P. J.; Lipton, R. B.; Ferrari, M. D. N. Engl. J. Med. 2002, 346, 257.
Silberstein, S. D. Lancet 2004, 363, 381.
Goadsby, P. J. Drugs 2005, 65, 2557.
Olesen, J.; Diener, H.-C.; Husstedt, I. W.; Goadsbyio, P. J.; Hall, D.; Meier, U.;
Pollentier, S.; Lesko, L. M. N. Engl. J. Med. 2004, 350, 1104.
g, h
O
H
2
N
SEM
N
N
5. (a) Paone, D. V.; Shaw, A. W.; Nguyen, D. N.; Burgey, C. S.; Deng, J. Z.; Kane, S. A.;
Koblan, K. S.; Salvatore, C. A.; Mosser, S. D.; Johnston, V. K.; Wong, B. K.; Miller-
Stein, C. M.; Hershey, J. C.; Graham, S. L.; Vacca, J. P.; Willimas, T. M. J. Med.
Chem. 2007, 50, 5564; (b) Ho, T. W.; Mannix, L.; Fan, X.; Assaid, C.; Furtek, C.;
Jones, C.; Lines, C.; Rapoport, A. Neurology 2008, 70, 1304; (c) Salvatore, C. A.;
Hershey, J. C.; Corcoran, H. A.; Fay, J. F.; Johnston, V. K.; Moore, E. L.; Mosser, S.
D.; Burgey, C. S.; Paone, D. V.; Shaw, A. W.; Graham, S. L.; Vacca, J. P.; Williams,
T. M.; Koblan, K. S.; Kane, S. A. J. Pharmacol. Exp. Ther. 2008, 324, 416.
6. Bell, I. M.; Bednar, R. A.; Fay, J. F.; Gallicchio, S. N.; Hochman, J. H.; McMasters,
D. R.; Miller-Stein, C.; Moore, E. L.; Mosser, S. D.; Pudvah, N. T.; Quigley, A. G.;
Salvatore, C. A.; Stump, C. A.; Theberge, C. R.; Wong, B. K.; Zartman, C. B.; Zhang,
X.-F.; Kane, S. A.; Graham, S. L.; Vacca, J. P.; Williams, T. M. Bioorg. Med. Chem.
Lett. 2006, 16, 6165.
i
O
H
2
N
NH
N
j
O
H
O
N
N
NH
N
N
O
O
7. Burgey, C. S.; Stump, C. A.; Nguyen, D. N.; Deng, J. Z.; Quigley, A. G.; Norton, B.
R.; Bell, I. M.; Mosser, S. D.; Salvatore, C. A.; Rutledge, R. Z.; Kane, S. A.; Koblan,
K. S.; Vacca, J. P.; Graham, S. L.; Williams, T. M. Bioorg. Med. Chem. Lett. 2006, 16,
N
2
7
Me
5
052.
Scheme 2. Synthesis of compound 27. Reagents and conditions: (a) BH
°C, 95%; (b) PBr , Et O, 99%; (c) NaH, SEMCl, DMF, 0 °C, 97%; (d) pyridine
hydrobromide perbromide, dioxane, 80%; (e) Zn, THF, sat. NH Cl, 75%; (f) Cs CO
DMF, 70%; (g) H , Pd/C, EtOH, 95%; (h) Chiralcel OD, MeOH, first major peak is (S)-
3
-THF, THF,
8
9
1
1
.
.
Stereochemistry established by X-ray crystallography on a derivative of the
corresponding aniline.
Theberge, C. R. et al Bioorg. Med. Chem. Lett. 2008, 18, 6122.
0
3
2
4
2
3
,
2
0. Clark, D. E. J. Pharm. Sci. 1999, 88, 807.
enantiomer; (i) HCl, MeOH, then NaOH, NH
EDC, HOBT, DIEA, DMF, 76%.
CH
2 2
2
CH NH
2
, MeOH, 79%; (j) RCO
2
H,
1. a All final compounds were characterized by 1H NMR, HPLC, and HRMS.
Additional synthetic details are provided in: (a) Bell, I. M.; Theberge, C. R.;
Stump, C. A.; Zhang, X. -F.; Gallicchio, S. N.; Zartman, C. B. WO 2006/031610.;
(
b) Bell, I. M.; Gallicchio, S. N.; Stump, C. A.; Theberge, C. R.; Vacca, J. P.;
Zartman, C. B.; Zhang, X. -F. WO 2006/031491.
12. Marfat, A.; Carta, M. P. Tetrahedron Lett. 1987, 28, 4027.
anomolar in the serum-shifted functional assay, representing a
000-fold improvement over the lead compounds 1 and 2. One
1